Problem: Simplify the following expression: $p = \dfrac{1}{8x} - \dfrac{1}{10x}$
In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $8x$ and $10x$ $\lcm(8x, 10x) = 40x$ $ p = \dfrac{5}{5} \cdot \dfrac{1}{8x} - \dfrac{4}{4} \cdot \dfrac{1}{10x} $ $p = \dfrac{5}{40x} - \dfrac{4}{40x}$ $p = \dfrac{5 -4}{40x}$ $p = \dfrac{1}{40x}$